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SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-K

(Mark One)

For the fiscal year ended December 31, 2003 or

For the transition period from              to             

Commission File Number 001-16611

MYKROLIS CORPORATION

(Exact name of registrant as specified in its charter)

(978) 436-6500

(Registrant’s telephone number, including area code)

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.  Yes  x    No  ¨

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of Form 10-K or any amendment to this Form 10-K.    ¨

Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Act).  Yes  x    No  ¨

As of June 30, 2003, the aggregate market value of the registrant’s voting stock held by non-affiliates of the registrant was approximately $402,923,950 based on the closing price on that date on the New York Stock Exchange.

As of January 31, 2004, 40,855,396 shares of the registrant’s Common Stock were outstanding.

Documents Incorporated by Reference

Part I

Item 1.    Business.

The Company

Mykrolis is a worldwide developer, manufacturer and supplier of liquid and gas delivery systems, components and consumables used to precisely measure, deliver, control and purify the process liquids, gases and chemicals that are used in the semiconductor manufacturing process. Our products are also used to manufacture a range of other products, such as flat panel displays, high purity chemicals, photoresists, solar cells, gas lasers, optical and magnetic storage devices and fiber optic cables. We sell our products worldwide through a direct sales force and through distributors in selected regions. Mykrolis Corporation was formed in 2000 in connection with the spin-off by Millipore Corporation of its microelectronics business unit. Our history is described in greater detail under “Our History” below.

We offer a diverse product line, grouped in 250 product categories, including both consumable products and equipment products. We also integrate consummable products and equipment components into subsystems that provide solutions to meet the liquid and gas delivery needs of our customers.

During the fourth quarter of 2003, Mykrolis acquired the business and certain of the assets and liabilities of Aeronex, Inc., a privately held company that developed, manufactured and marketed gas purification components and systems. The Aeronex products complement our line of gas purifiers. Aeronex’s results of operations are included in our consolidated and combined financial statements since October 27, 2003, the date of purchase.

Unless the context otherwise requires, the terms “Mykrolis”, “we”, “our”, or the “Company” mean Mykrolis Corporation and its subsidiaries and the term “Millipore” means Millipore Corporation and its subsidiaries when referring to periods prior to March 31, 2001 and Millipore Corporation and its subsidiaries other than Mykrolis when referring to periods subsequent to March 31, 2001.

Background

The manufacture of semiconductors requires hundreds of process steps which take place in the controlled environment of process chambers within the semiconductor tool. We offer products for each of the primary processing steps in the manufacture of semiconductors which are listed below.

Deposition.    Deposition refers to placing layers of insulating or conductive materials on a wafer surface in thin films that make up the circuit elements of semiconductor devices. The two main deposition processes are physical vapor deposition, where a thin film is deposited on a wafer surface in a low-pressure gas environment, and chemical vapor deposition, where a thin film is deposited on a wafer surface using a gas medium and a chemical bonding process. In addition, electro-plating technology is utilized for the deposition of low resistance conductive materials such as copper. The control of uniformity and thickness of these films through filtration and purification of the fluids and materials used during the process is critical to the performance of the semiconductor circuit and, consequently, the manufacturing yield.

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Chemical Mechanical Planarization.    Chemical mechanical planarization flattens, or planarizes, the topography of the film surface to permit the patterning of small features on the resulting smooth surface by the photolithography process. Semiconductor manufacturers need filtration and purification systems to maintain acceptable manufacturing yields through the chemical mechanical planarization process by filtering the liquid slurries, which are solutions containing abrasive particles in a chemical mixture, to remove oversized particles and contaminants that can cause defects on a wafer’s surface while not affecting the functioning of the abrasive particles in the liquid slurries.

Photolithography.    Photolithography is the process step that defines the patterns of the circuits to be built on the chip. Before photolithography, a wafer is pre-coated with photoresist, a light sensitive film composed of ultra-high purity chemicals in liquid form. The photoresist is exposed to specific forms of radiation, such as ultraviolet light, electrons or x-rays, to form patterns which eventually become the circuitry on the chip. This process is repeated many times, using different patterns and interconnects between layers to form the complex, multi-layer circuitry on a semiconductor chip. As device geometries decrease and wafer sizes increase, it is even more critical that these photoresists are dispensed on to the chip with accurate thickness and uniformity, as well as with low levels of contamination, and that the process gases are free of micro-contamination so that manufacturers can achieve acceptable yields in the manufacturing process.

Etch and Resist Strip.    Etch is the process of selectively removing precise areas of thin films that have been deposited on the surface of a wafer. The hardened photoresist protects the remaining material that makes up the circuits. During etch, specific areas of the film not covered by photoresist are removed to leave a desired circuit pattern. Similarly, resist strip is a process of removing the photoresist material from the wafer after the desired pattern has been placed on the wafer. Emerging advanced etch and resist strip applications require precisely controlled gas chemistries and flow rates in order to achieve precise etch and resist strip characteristics.

Wet Cleaning.    Ultra-high purity chemicals and photoresists of precise composition are used to clean the wafers, to pattern circuit images and to remove photoresists after etch. Before processes such as photoresist coating, thin film deposition, ion implantation, diffusion and oxidation, and after processes, such as ion implantation and etch, the photoresists must be stripped off, and the wafer cleaned in multiple steps of chemical processes. To maintain manufacturing yields and avoid defective products, these chemicals must be maintained at very high purity levels without the presence of foreign material such as particles, ions or organic contaminants.

The increasing complexity of semiconductor devices has resulted in the need for more complex, higher-precision liquid and gas delivery, measurement, control and purification systems and subsystems. The ability of semiconductor device manufacturers to offer integrated circuits with smaller geometries, greater functionality and higher performance at a lower cost requires continuous improvements in semiconductor process equipment, process controls and liquid and gas delivery systems. The design and performance of those liquid and gas delivery systems, subsystems, components and consumables are critical to the semiconductor manufacturing process because they directly affect cost of ownership and manufacturing yields.

In addition, as equipment and process complexity in semiconductor manufacturing increases, semiconductor original equipment manufacturers and device manufacturers are seeking to improve time-to-market, reduce manufacturing costs, improve production quality and enhance product reliability and long-term service and support. To address these challenges, semiconductor equipment companies and device manufacturers are outsourcing the design and manufacture of liquid and gas delivery, measurement, control and purification systems, subsystems, components, and consumables to us and to other well-established subsystem and component companies that have worldwide presence and leading technologies.

Many of the processes used to manufacture semiconductors are also used to manufacture flat panel displays, magnetic and optical storage devices and fiber optic cables for telecommunications, resulting in the need for similar filtration, purification, control and measurement capabilities.

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Our Business Strategy

Our objective is to be a global leader providing innovative process solutions to the semiconductor and ancillary markets. We intend to build upon our position as a worldwide developer, manufacturer and supplier of liquid and gas delivery systems, components and consumables used by semiconductor and other electronic device manufacturers to grow our business in these and other high value-added manufacturing process markets. Our strategy includes the following key elements:

Comprehensive and Diverse Product Offerings.    The semiconductor manufacturing industry is driven by rapid technological changes and intense competition. We believe that semiconductor manufacturers are seeking process control suppliers who can provide a broad range of reliable, flexible and cost effective products, as well as the technological and application design expertise necessary to deliver effective solutions. Our comprehensive product offerings enable us to meet a broad range of customer needs and provide a single source of flexible product offerings for semiconductor device and capital equipment manufacturers as they seek to consolidate their supplier relationships to a smaller select group. In addition, we believe manufacturers of semiconductor tools are looking to their suppliers for subsystems that provide more integrated functionality and that can seamlessly communicate with other equipment. We believe our offering of consumables and equipment, as well as our ability to integrate them, allows us to provide advanced subsystems.

Diversified Revenue Stream.    We target a diversified revenue stream by balancing our sales of component and subsystem equipment products with sales of our consumable products. Our consumable products provide a relatively more stable and recurring source of revenue in an otherwise cyclical industry. Our equipment products, sales of which are generally driven by such factors as the construction and expansion of semiconductor manufacturing facilities and the retrofitting and renovation of existing semiconductor facilities, position us to benefit from increases in capital spending that typically occur during industry upturns.

Technology Leadership.    With the emergence of smaller and more powerful semiconductor devices, and the deployment of new materials and processes to produce them, we believe there is a need for greater contamination and process control within the semiconductor fabrication process. We seek to extend our technology by developing advanced products that address more stringent requirements for greater contamination control, fluid delivery and monitoring, and system integration. We have continuously improved our products as our customers’ needs have evolved. For example, we have expanded upon our proprietary two-stage dispense technology with integrated filtration for photoresist delivery, where the photoresist is filtered through one pump and precisely dispensed through a second pump at a different flow rate to reduce defects on wafers.

Strong Customer Base.    We have established ongoing relationships with many leading semiconductor device manufacturers and original equipment manufacturers, gas and chemical manufacturing companies and manufacturers of high precision electronics. These industry relationships have provided us with the opportunity for significant collaboration with our customers at the product design stage which has facilitated our ability to introduce new products and applications that meet our customers’ needs. For example, we work with our key customers at the pre-design and design stage to identify and respond to their requests for current and future generations of products. We target opportunities to offer new technologies in emerging applications, such as copper plating, chemical mechanical planarization, wet and dry cleaning systems and photolithography. We believe that our large customer base will continue to be an important source of new product development ideas.

Global Presence.    We have established a global infrastructure of design, manufacturing, distribution, service and support facilities to meet the needs of our customers. In addition, we may expand our global infrastructure, either through acquisition or internal development, to accommodate increased demand or we may consolidate inefficient operations to optimize our manufacturing and other capabilities. For example, we have established sales and service offices in China in anticipation of a growing semiconductor manufacturing base in that region. As semiconductor and other electronic device manufacturers have become increasingly global, they have required that suppliers offer comprehensive local repair and customer support services. We maintain our customer relationships through a combination of direct sales and support personnel and selected independent sales representatives and distributors in Asia, Europe and the Middle East.

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Ancillary Markets.    We plan to leverage our accumulated expertise in the semiconductor industry by developing products for applications that employ similar production processes that utilize high purity fluids, integrated dispense systems and vacuum-based production technologies. Our products are used in manufacturing processes outside of the semiconductor industry, including the manufacturing of flat panel displays, high-purity chemicals, photoresists, solar cells, gas lasers, optical and magnetic storage devices and fiber optic cables. We plan to continue to identify and develop products that address advanced materials processing applications where fluid management plays a critical role. We believe that by utilizing our technology to provide manufacturing solutions across multiple industries we are able to increase the total available market for our products and reduce, to an extent, our exposure to the cyclicality of any particular market. In addition, as the dynamics of the markets that we serve shift, we will re-evaluate the ability of our existing businesses to provide value added solutions to those markets in a manner that contributes to our achieving our objective; in the event that we conclude that a business is not able to do this, we expect to restructure or replace that business.

Strategic Acquisitions and Partnerships.    We plan to pursue strategic acquisitions and business partnerships that enable us to address gaps in our product offerings, secure new customers, diversify into complementary product markets or broaden our technological capabilities and product offerings. During the fourth quarter of 2003, we acquired the business and certain of the assets and liabilities of Aeronex, Inc., a privately held company that developed, manufactured and marketed gas purification components and systems. In addition, we are continuously evaluating opportunities for strategic alliances and joint development efforts with key customers and other industry leaders.

Products

Our products include consumable products and equipment products that are used in the manufacture of semiconductors and other high precision electronic devices. Our consumable products include liquid filtration and purification products and gas filtration and purification products as well as other filtration components and service programs. Our equipment products include precision liquid dispense systems, mass flow and pressure controllers, gas purification systems and vacuum gauges. These products are used by customers in manufacturing operations to remove contaminants in liquid and gas processes, to purify liquids and gases, to measure and control flow rates and to control and monitor pressure and vacuum levels during the manufacturing process. In addition, we integrate consumable products and equipment components into subsystems that provide our customers with integrated solutions to meet a particular liquid and gas needs. Consumable products, including service revenue, accounted for 71%, 65% and 58%, of our net sales for the years ended December 31, 2003, 2002, and 2001, respectively, and equipment products accounted for 29%, 35% and 42%, respectively, of our net sales in these same periods. In each of these periods liquid filtration and purification products accounted for more than two-thirds of our net sales from consumable products. For the years ended December 31, 2003, 2002 and 2001, our gas delivery products accounted for approximately 55%, 54% and 61%, respectively, of our net sales from equipment products. Our two product classes include the following specific product types:

Consumable Products

Our consumable products include membrane based liquid filters and housings, metal based gas filters and resin based gas purifiers, which purify the process fluids used in the semiconductor manufacturing process. The key drivers of demand for our consumable products include the utilization rate of semiconductor fabrication facilities, the number of semiconductor wafers being manufactured and the timing of semiconductor plant preventative maintenance programs during which filters are usually replaced.

Liquid Filtration and Purification Products

Liquid processing occurs during multiple manufacturing steps including photolithography, deposition, planarization and surface etching and cleaning. The fluids that are used include various mixtures of acids, bases, solvents, slurries and photochemicals, which in turn are used over a broad range of operating conditions,

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including temperatures from 5 degrees Celsius up to 180 degrees Celsius. The design and performance of our liquid filtration and purification products are critical to the semiconductor manufacturing process because they directly affect the cost of ownership and manufacturing yield. Specially designed proprietary filters remove sub-micron sized particles and bubbles from the different fluid streams that are used in the manufacturing process. Some of our filters are constructed with ultra-high molecular weight polyethylene hollow fiber and flat sheet membranes that offer improved bubble clearance and gel removal, either of which can cause defects in the wafers if not removed. Our low hold-up volume disposable filters, with hollow fiber or flat sheet membranes, use our Connectology^™ technology to allow filter changes in less than a minute, significantly faster than conventional filters, to reduce the amount of expensive chemicals lost each time a filter is changed and to minimize operator exposure to hazardous solvents and vapors during changeout.

Gas Filtration and Purification Products

Our Wafergard^®, ChamberGard^™ and Waferpure^® particle and molecular filtration products purify the gas entering the process chamber in order to eliminate system and wafer problems due to particulate, atmospheric and chemical contaminants. These filters are able to retain substantially all particles 0.003 microns and larger. Our metal filters, such as stainless steel and nickel filters, reduce outgassing and improve corrosion resistance. Our Waferpure^® and Aeronex Gatekeeper^® purifiers chemically react with and absorb volatile contaminants, such as oxygen and water, to prevent contamination and our ChamberGard^™ vent diffusers reduce particle contamination and processing cycle times.

Equipment

Our equipment products include precision liquid dispense systems, mass flow and pressure controllers, gas purification systems and vacuum gauges as well as other equipment components. The key drivers of demand for our equipment products include the expansion and construction of semiconductor fabrication facilities, retrofitting and renovation of existing semiconductor production equipment and the installation of new processes in semiconductor fabrication facilities.

Liquid Delivery Systems

Our proprietary photochemical filtration and dispense systems integrate our patented two-stage, filter device and valve control technologies. We believe that we offer the microelectronics industry the only integrated filtration and dispense systems and that our proprietary patented two-stage technology has a significant advantage over conventional single-stage technology. Our two-stage technology permits the filtering and dispense functions to operate independently so that filtering and dispensing of photochemicals can occur at different rates, reducing the differential pressure across the filter, conserving expensive photochemicals and resulting in reduced defects in wafers. As described above, we offer a line of proprietary filters specifically designed to efficiently connect with our liquid delivery systems. Our patented digital valve control technology improves chemical uniformity on wafers and improves ease of optimized system operation. In addition, our integrated high precision liquid dispense systems enable uniform application of photoresists for the spin-coating process where uniformity is measured in units of Angstroms, a tiny fraction of the thickness of a human hair.

Gas Delivery Products and Purification Systems

We offer a wide variety of gas delivery and purification products to meet the stringent requirements of semiconductor processing, including mass flow controllers, transducers, vacuum gauges, valves and controllers and gas purification systems.

Our mass flow controllers automatically and precisely measure and control the flow rates of multiple liquids and gases into the semiconductor tool process chamber in order to maintain circuit quality, reduce maintenance requirements and prolong the life of the equipment used in the manufacturing process. We have also developed

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pressure-based mass flow controllers, which measure and control the liquids and gases by controlling the pressure applied to these fluids. Our IntelliFlow^® product platform combines our gas measurement and control products with the DeviceNet^™ communications protocol to provide a digital solution to achieve advanced process control and network communications to provide real time feedback as to gas measurement and control performance, thereby minimizing costly unscheduled down time.

Our Aeronex Infinity^™ Gas Purification Systems contain dual resin beds providing a continuous supply of purified gas without process interruption. These gas purification systems are capable of handling higher flow rates and longer duty cycles than cartridge purifiers.

We also offer other equipment components including: transducers to measure the pressure in the process gas feed line and of the process fluids during semiconductor manufacturing; vacuum gauges to directly measure the level of pressure in the process chamber and between the process chamber and a pump; and vacuum controllers to receive signals from the vacuum gauges and provide the necessary control signals to the vacuum valves in order to maintain precise processing parameters.

We believe that our customers will increasingly demand more integrated products and systems that combine the functionality of many of our gas delivery products which were previously purchased as discrete components.

Worldwide Applications Development and Field Support Capabilities

We provide strong technical support to our customers through local service groups and engineers consisting of field applications engineers, technical service groups, applications development groups and training capabilities. Our field applications engineers, located in the United States and in eight other countries, work directly with our customers on product qualification and process improvement in their facilities. In addition, in response to customer needs for local technical service and fast turn-around time, we maintain regional applications laboratories. Our applications laboratories maintain process equipment that simulate customers’ applications and industry test standards and provide product evaluation, technical support and complaint resolution for our customers. Our service centers are responsible for calibration, repairs and servicing of our products. These service centers also support industry collaborations and provide additional technical expertise to our customers. We have service centers located in California, Texas, Japan, Korea, China, Taiwan, Singapore, Germany and France.

Customers and Markets

Our major customer groups include semiconductor device manufacturers, original equipment manufacturers that provide equipment to semiconductor device manufacturers, gas and chemical manufacturing companies and manufacturers of high precision electronics.

Our most significant customers based on sales in 2003 include industry leaders, such as Applied Materials, Inc., Dainippon Screen Manufacturing Co., Ltd., Samsung Electronics Co., Ltd., Taiwan Semiconductor Manufacturing Co. Ltd., Tokyo Electron Limited and UMC Group. We also sell our products to flat panel display original equipment manufacturers, materials suppliers and end-users. The major manufacturers for flat panel displays and flat panel display equipment are concentrated in Japan, Korea and other parts of Asia.

In 2003, 2002 and 2001, net sales to our top ten customers accounted for approximately 34%, 35% and 33%, respectively, of our net sales. During those same periods, our largest single customer accounted for approximately 11%, 13% and 14%, respectively, of our net sales and international net sales represented approximately 73%, 69% and 67%, respectively, of our net sales. Over 2,700 customers purchased products from us during 2003.

We may enter into supply agreements with our customers to govern the conduct of business between us and our customers, including the manufacture of our products. These agreements generally have a term of one to

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three years but these agreements do not contain any long-term purchase orders or commitments. Instead, we work closely with our customers to develop non-binding forecasts of the future volume of orders. However, customers may cancel their orders, change production quantities from forecasted volumes or delay production for a number of reasons beyond our control.

Sales and Marketing

We sell our products worldwide primarily through our own direct sales force located in twelve offices in all major semiconductor markets, as well as through independent distributors elsewhere. As of December 31, 2003, our sales and marketing force consisted of approximately 180 employees worldwide. Our direct sales force is supplemented by independent sales representatives and agents.

Our marketing efforts focus on our “push/pull” marketing strategy in order to maximize our selling opportunities. We work with original equipment manufacturers who design tools that require our products and we create end user demand where the products are specified by the semiconductor manufacturers. Our industry relationships have provided us with the opportunity for significant collaboration with our customers at the product design stage that has facilitated our ability to introduce new products and applications that meet our customers’ needs. In addition, we are constantly identifying for our customers the variety of analytical, purification and process control challenges which may be addressed by our products. Further, we adapt our products and technologies to process control issues identified by our customers. Our sales representatives provide our customers with worldwide support and information about our products.

We believe that our technical support services are important to our marketing efforts. These services include assisting in defining a customer’s needs, evaluating alternative products, designing a specific system to perform the desired separation, training users and assisting customers in compliance with relevant government regulations. In addition, we maintain a network of service centers located in the United States and in key international markets to support our products.

Competition

The market for our products is highly competitive. While price is an important factor, we compete primarily on the basis of the following factors:

We believe that we compete favorably with respect to all of the factors listed above, but we cannot assure you that we will continue to do so. We believe that our key competitive strengths include our broad product line, the low total cost of ownership of our products, our ability to provide our customers with quick order fulfillment and our technical expertise. However, our competitive position varies depending on the market segment and specific product areas within these segments. For example, in the market for photochemical dispense systems, we believe that our patented technology, our longstanding relationship with the leading original equipment manufacturer in this market niche and our ability to support our customers’ needs on a global basis have allowed us to compete favorably. In contrast, other companies have more established positions in the markets related to gas delivery systems and components, such as gas flow measurement and control products, pressure measurement and control products and vacuum gauges, valves and controllers. While we have longstanding relationships with a number of semiconductor and other electronic device manufacturers, we also face significant competition from

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companies that have longstanding relationships with other semiconductor and electronic device manufacturers and, as a result, have been able to have their products specified by those customers for use in manufacturers’ fabrication facilities. In addition, some of our competitors have cost advantages over us in the markets for gas delivery systems and components due to their larger market share and the related economies of scale. In the markets for our consumable products, we believe that our differentiated membrane technology, strong supply chain capabilities, which allow us to provide our customers with quick order fulfillment, and technical expertise, which enables us to develop membranes to meet specific customer needs and assist our customers in improving the functionality of our membranes for particular applications, allow us to compete favorably. In these markets our competitors compete against us on the basis of price, as well as alternative membrane technology having different functionality, manufacturing capabilities and breadth of geographic presence.

The market for our products is highly fragmented, and we compete with a number of different companies, including Advanced Energy Industries Inc., Celerity Group, Inc., Iwaki Co., Ltd., MKS Instruments, Inc., Mott Metallurgical Corporation and Pall Corporation. Some of our competitors are larger and have greater resources than we do. In some cases, our competitors are smaller than us, but well-established in specific product niches. However, we believe that none of our competitors competes with us across all of our product offerings and that, within the markets that we serve, we offer a broader line of products, make use of a wider range of process control technologies and address a broader range of applications than any single competitor. Nonetheless, competitors with greater financial resources may be able to offer lower prices, additional products or services or other incentives that we cannot match or offer. These competitors may be in a stronger position to respond quickly to new technological trends, devote more resources to capitalize on those new technological trends and may be able to undertake more extensive marketing campaigns. They also may adopt more aggressive pricing policies and make more attractive offers to potential customers, employees and strategic partners.

Semiconductor and other electronic device manufacturers may direct semiconductor capital equipment manufacturers to use a specified supplier’s product in their equipment. Accordingly, our success depends in part on our ability to have semiconductor and other electronic device manufacturers specify that our products be used at their fabrication facilities. Some of our competitors may have more developed relationships with semiconductor and other electronic device manufacturers, which enable them to have their products specified for use in manufacturers’ fabrication facilities.

Research and Development

Our aggregate research and development expenses in 2003, 2002 and 2001 were $19.1 million, $19.7 million and $19.8 million, respectively. As of December 31, 2003, we had approximately 102 employees in engineering, research and development. In addition, we have followed a practice of supplementing our internal research and development efforts by licensing technology from unaffiliated third parties and/or acquiring distribution rights with respect thereto when we believe it is in our long-term interests to do so.

To meet the global needs of our customers, we have research and development capabilities in the United States and Japan. Our research and development efforts are directed toward developing and improving our technology platforms for semiconductor and advanced processing applications and identifying and developing products for new applications for which fluid management plays a critical role. Key elements of our 2003 and 2002 research development expenses were related to the development of the new product platforms to meet the manufacturing needs for 90 and 65 nanometer semiconductor devices. Driven by the proliferation of new materials and chemicals in the manufacturing processes, and increased needs for tighter process control for 300mm wafers, investments were made for new contamination control products in area of copper interconnects, deep ultra-violet (DUV) photolithography; and chemical and gas management technologies for advanced wafer cleans, deposition and etch equipment. Additional investments were made in area of advanced process control, monitoring and diagnostics capabilities for future generations of semiconductor manufacturing processes. We have undertaken an initiative to involve our marketing, engineering, manufacturing and sales personnel in the development of new products in order to reduce the time to market for new products. Our employees also work

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closely with our customers’ development personnel. These relationships help us identify and define future technical needs on which to focus our research and development efforts. In addition, we participate in Semiconductor Equipment and Materials International (SEMI), a consortium of semiconductor equipment suppliers. We also support research at academic and other institutions targeted at advances in materials science and semiconductor process development. Finally we continue to maintain a membrane research agreement with Millipore that was entered into at the time of our separation from Millipore and continues in effect through March 31, 2006.

Patents and Other Intellectual Property Rights

We rely on a combination of patent, copyright, trademark and trade secret laws and license agreements to establish and protect our proprietary rights. We maintain 130 U.S. issued and enforceable patents, 182 issued and enforceable foreign patents, including counterparts to U.S. filings, 102 pending U.S. patent applications, 29 pending filings under the Patent Cooperation Treaty not yet nationalized and 298 pending foreign patent applications. While we believe that patents may be important for aspects of our business, such as our patents related to photoresist dispense pumps, polymeric membranes and surface chemistries, gas filters and purifiers, gas and liquid contactors, fluid control processes, mass flow controllers and our Connectology^™ products, which U.S. patents expire between 2005 and 2022, we believe that our success also depends more upon close customer contact, innovation, technological expertise, responsiveness and worldwide distribution. Additionally, while our patented technology may delay or deter a competitor in offering a competing product, we do not believe that our patent portfolio functions as a barrier to entry for any of our competitors. In addition, while we license and will continue to license technology used in the manufacture and distribution of products from third parties, except as described in the “Risks Related to our Separation from Millipore” section of Management’s Discussion and Analysis of Financial Condition and Results of Operations in Item 7 below, which information is hereby incorporated by reference, these licenses are not currently related to any of our core product technology.

We require each of our employees, including our executive officers, to enter into standard agreements pursuant to which the employee agrees to keep confidential all of our proprietary information and to assign to us all inventions made while employed by us.

A number of our patented products were specifically developed in response to the transition from 200 millimeter wafers to 300 millimeter wafers, and many of our new products are specifically targeted to meet the more stringent requirements for the advanced technologies dominating 300 millimeter wafer manufacturing processes. Examples include our Solaris^® chemical mechanical planarization filters for copper slurries, IntelliGen^® photoresist dispense with digital valves targeted for photolithography applications and our IntelliFlow^® mass flow controllers for 300 millimeter tool automation.

In connection with our separation from Millipore, we were assigned patents and trademarks which relate exclusively to our business. Patented technology that was used by both Millipore and Mykrolis was generally retained by Millipore and licensed to us with exclusive rights in our fields of use that are generally defined by the operating scope of our business at the time of our separation from Millipore. In some cases, the technology was transferred to us, and we granted Millipore an exclusive license in its fields of use in the biopharmaceutical and related industries. These licenses are assignable by the licensee only in connection with a sale of its business, do not require the payment of any license fees or royalties by either Millipore or us and will continue in effect for the life of the patents. In addition, in order to assure future access to patented technology not licensed as part of the separation, the separation agreements provide each of us with a technology license option. The option grants each party a five-year option to acquire a royalty bearing license to patented technology existing as of the separation date that is owned by the other party and is not currently used by the optionee but may be useful for future products, with exclusive rights in its fields of use. The license term would extend for the life of the subject patents.

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Governmental Regulation

Our operations are subject to federal, state and local regulatory requirements relating to environmental, waste management and health and safety matters, including measures relating to the release, use, storage, treatment, transportation, discharge, disposal and remediation of contaminants, hazardous substances and wastes, as well as practices and procedures applicable to the construction and operation of our plants. There can be no assurance that we will not incur material costs and liabilities or that our past or future operations will not result in exposure to injury or claims of injury by employees or the public. Although some risk of costs and liabilities related to these matters is inherent in our business, as with many similar businesses, we believe that our business is operated in substantial compliance with applicable regulations. However, new, modified or more stringent requirements or enforcement policies could be adopted, which could adversely affect us. While we expect that capital expenditures will be necessary to assure that any new manufacturing facility is in compliance with environmental and health and safety laws, we do not expect these expenditures to be material. Otherwise, we are not presently aware of any facts or circumstances that would cause us to incur significant liabilities in the future related to environmental, health and safety law compliance.

Employees

As of February 1, 2004, we had approximately 877 full-time employees, including approximately 102 in engineering, research and development and approximately 180 in sales and marketing. Given the variability of business cycles in the semiconductor industry and the quick response time required by our customers, it is critical that we be able to quickly adjust the size of our production staff to maximize efficiency. Therefore, we use skilled temporary labor as required. In connection with our separation from Millipore, we hired personnel to facilitate our operation as an independent company and in replacement of services formerly provided by Millipore’s central functions.

None of our employees are represented by a labor union or covered by a collective bargaining agreement other than statutorily mandated programs in European countries.

Information About Our Operating Segment

The Company operates in one reportable business segment that develops, manufactures and sells consumables and capital equipment products to semiconductor manufacturing companies and other companies using similar manufacturing processes, as well as Original Equipment Manufacturer (“OEM”) suppliers to those companies. In 2003, 2002 and 2001 approximately 73%, 69% and 67%, respectively, of our net sales were made to customers outside North America. Industry and geographic segment information is discussed in Note 14 to the Mykrolis Corporation Consolidated and Combined Financial Statements (the “Financial Statements”) included in Item 8 below, which Note is hereby incorporated herein by reference.

Other Information

In March of 2001, the Board of Directors of Mykrolis adopted a shareholder rights plan (the “Rights Plan”) pursuant to which Mykrolis declared a dividend on November 29, 2001 to its shareholders of record on December 31, 2001 of the right to purchase (a “Right”) one additional share of Mykrolis Common Stock for each share of Mykrolis Common Stock owned, at a price of $130.00 for each share. The Rights Plan is designed to protect Mykrolis’ shareholders from attempts by others to acquire Mykrolis on terms or by using tactics that could deny all shareholders the opportunity to realize the full value of their investment. The Rights are attached to the shares of our common stock until certain triggering events occur. The Rights authorize the holders to purchase shares of our common stock at a 50% discount from market value upon the occurrence of specified triggering events, including, unless approved by our board of directors, an acquisition by a person or group of specified levels of beneficial ownership of our common stock or a tender offer for our common stock. The common stock purchase rights are redeemable by us for $0.01 and will expire in March of 2011. One of the

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events which will trigger the common stock purchase rights is the acquisition, or commencement of a tender offer, by a person (an Acquiring Person, as defined in the shareholder rights plan), other than Mykrolis or any of our subsidiaries or employee benefit plans, of 15% or more of the outstanding shares of our common stock. An Acquiring Person may not exercise a common stock purchase right.

Mykrolis’ products are made from a wide variety of raw materials which are generally available in quantity from alternate sources of supply. Accordingly, as a general matter, Mykrolis is not substantially dependent upon any single supplier.

Our History

Mykrolis Corporation is a Delaware corporation organized on October 16, 2000 under the name Millipore MicroElectronics, Inc. in connection with the spin-off by Millipore Corporation of its microelectronics business unit. On March 27, 2001, we changed our name to Mykrolis Corporation. On March 31, 2001, Millipore effected the separation of our business from Millipore’s business by transferring to us substantially all of the assets and liabilities associated with its microelectronics business. On August 9, 2001 we completed an initial public offering of approximately 18% of the total shares of the Company’s common stock outstanding. On February 27, 2002, Millipore completed the spin-off of Mykrolis by distributing to its stockholders the 82% of our common stock that it held following our initial public offering. In the early 1980’s, Millipore internally developed products with applications in semiconductor manufacturing, which became the Millipore microelectronics business unit. Subsequently, through internal development and acquisitions, Millipore expanded that business unit into the business that was spun off as Mykrolis Corporation.

Executive Officers of Mykrolis

The following is a list, as of February 1, 2004, of the Executive Officers of Mykrolis. All of the officers of Mykrolis Corporation listed below were elected to serve until the first Directors Meeting following the 2004 Annual Stockholders Meeting.

C. William Zadel has been our Chairman and Chief Executive Officer since November 2000 and one of our directors since February 2001. Mr. Zadel was Chief Executive Officer, Chairman and President of Millipore from February 1996 through April 2001, at which time he resigned as President but continued as Chief Executive Officer until August 2001. Mr. Zadel continued to serve Millipore as a non-executive Chairman of the Board and a director until April 2002. Mr. Zadel had been, since 1986, President and Chief Executive Officer of Ciba Corning Diagnostics Corp., a company that develops, manufactures and sells medical diagnostic products. Prior

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to that he was Senior Vice President of Corning Glass Works (now Corning Inc.) Americas Operations since 1985 and Vice President of business development since 1983. Mr. Zadel currently serves on the Boards of Directors of Kulicke and Soffa Industries, Inc. and Matritech, Inc. Mr. Zadel is a Director (Chairman 1999-2001) of the Massachusetts High Technology Council. He has also served as the Chairman of the Health Industry Manufacturers Association from 1994 to 1995.

Jean-Marc Pandraud has been our President and Chief Operating Officer since January 2001. Prior to that he served as Vice President and General Manager of the Microelectronics Divisions of Millipore, a position he had held since July 1999. From 1994 until 1999, Mr. Pandraud served as the Vice President and General Manager of Millipore’s Laboratory Water Division and was also Regional Manager of Millipore’s Latin American operations from 1997 until 1999. Mr. Pandraud also served as the Managing Director of Millipore’s French subsidiary and as European General Manager for the Millipore Analytical Division from 1988 until 1994.

Bertrand Loy has been our Vice President and Chief Financial Officer since January 2001. Prior to that, Mr. Loy served as the Chief Information Officer of Millipore from April 1999 until December 2000. From 1995 until 1999, he served as the Division Controller for Millipore’s Laboratory Water Division. From 1989 until 1995, Mr. Loy served Sandoz Pharmaceuticals (now Novartis) in a variety of financial, audit and controller positions located in Europe, Central America and Japan.

Peter W. Walcott has been our Vice President, Secretary and General Counsel since October 2000. Mr. Walcott served as the Assistant General Counsel of Millipore from 1981 until March 2001.

Fred E. Faulkner, Jr. has been our Vice President—Worldwide Manufacturing since April 2001. Prior to joining Mykrolis, Mr. Faulkner served as Millipore’s Director of Manufacturing Operations from May 2000 until April 2001. Prior to that, Mr. Faulkner was President and Chief Operating Officer of Boston Acoustics, Inc., a designer and manufacturer of high-performance audio systems, from April 1997 until April 2000. Before joining Boston Acoustics, Mr. Faulkner served as Vice President of Technical Operations for Millipore’s Microelectronics Division from June 1994 until April 1997.

Takashi Mizuno has been our Vice President since April 2001 and has been President of our Japanese subsidiary, Nihon Mykrolis KK since April 2001. Mr. Mizuno was a Director of Global Accounts for Tokyo Electron Limited from February 2000 until April 2001. Prior to that, Mr. Mizuno served as Millipore’s Director of Laboratory Research from September 1995 until February 2000 and as Division Manager of Millipore’s Laboratory Water Division from January 1995 until September 1995.

Gerry Mackay has been our Vice President—Worldwide Sales & Marketing since February 2002. Prior to joining Mykrolis, Mr. Mackay served Millipore in various sales and marketing capacities since August of 1987, first with Millipore’s UK subsidiary and subsequently as the General Manager for Millipore’s Asia operations and finally as Worldwide Director of Marketing—Biotechnology. Mr. Mackay was designated as an Executive Officer by our Board of Directors in April 2002, and was elected an officer of the corporation in April 2003.

Jieh Hwa Shyu has been our Vice President of Research and Development since April of 2001, was designated as an Executive Officer by our Board of Directors in April 2002 and was elected an officer of the corporation in April 2003. In January 2004 Mr. Shyu was named Chief Technology Officer of Mykrolis. Prior to our separation from Millipore, Mr. Shyu served the Microelectronic Division of Millipore as a Director of R & D from 1997 until March 2001. Prior to joining Millipore, Mr. Shyu served Digital Equipment Corporation as a Principal Engineer and Supervisor.

Sharon Pinto has been our Vice President—Human Resources since June of 2003 and was designated as an Executive Officer by our Board of Directors in October 2003. Prior to joining us Ms. Pinto had served as the Director of Human Resources at Maxtor Corporation since April 2002. From January 2001 until April 2002, Ms. Pinto was the Director of Human Resources at Tilion Inc and from January 1999 until December of 2000 she

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served as the Global Human Resource Director of Lionbridge Technologies Inc. Prior to that Ms. Pinto was a Senior Human Resources Manager at Polaroid Corporation.

Available Information

Our Annual Report on Form 10-K, our quarterly reports on Form 10-Q and any current reports on Form 8-K that we may file or furnish to the S.E.C. pursuant to Sections 13(a) or 15(d) of the Securities Exchange Act of 1934 as well as any amendments to any of those reports are available free of charge on or through our website as soon as reasonably practicable after we file them with or furnish them to the S.E.C. electronically. Our website is located at http://www.Mykrolis.com; these reports can be found under “Investor Relations—SEC Filings”.

The Board of Directors adopted an amended code of business ethics, The Mykrolis Code of Conduct, applicable to all of our executives, directors and employees on June 27, 2002 as well as a set of corporate governance guidelines on December 19, 2002. The Mykrolis Code of Conduct, the Governance Guidelines and the charters for our Audit & Finance Committee and of our Management Development & Compensation Committee all appear on our website at http://www.Mykrolis.com under “Investor Relations—Governance”. The Governance Guidelines and committee charters are also available in print to any shareholder that requests a copy. Copies may be obtained by contacting Peter W. Walcott, our Vice President & General Counsel at our corporate headquarters.

Item 2.    Properties.

Our principal executive offices are located in Billerica, Massachusetts. We also have manufacturing and design facilities in the United States and Japan. Information about these facilities is set forth below:

In addition, we lease a 144,000 square foot building in Bedford, Massachusetts of which 70,000 square feet is subleased by us to a third party under a sublease expiring in November 2005. We have an option to purchase this leased facility at fair market value between June 2005 and November 2005, the expiration date on our lease, and our landlord has an option to sell us this facility at 90% of its fair market value prior to November 30, 2005. If our landlord exercises the option to sell, we will have one year to complete the purchase of the facility, during which time interest on the purchase price will accrue. Since this facility was deemed to be inappropriate for our business needs, we closed this facility during the third quarter of 2001. We are currently attempting to sublease the unused portion of this facility.

We lease approximately 4,200 square feet of manufacturing space in Millipore’s facility located at 80 Ashby Road, Bedford, MA under a transitional services agreement that expires March 31, 2006. We also lease approximately 21,000 square feet of research and development and manufacturing space in two buildings located in San Diego, California which we assumed pursuant to our acquisition of Aeronex, Inc. described above. The leases for this space expire in October 2004 and January 2005.

We maintain a worldwide network of sales and service centers, including two in the United States, two in Europe (one in Germany and one in France), two in Japan and five in other parts of Asia (Taiwan, Singapore,

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China (Shanghai) and Korea). Leases for our facilities expire between February 2004 and March 2014. We currently expect to be able to extend the terms of expiring leases or to find suitable replacement facilities on reasonable terms.

We believe that our facilities are well-maintained and, except as described above, suitable for their respective operations. Except for approximately 25,000 square feet in our Billerica facility, 27,000 square feet in our Yonezawa plant, our Swindon U.K. site and the above described closed facility, all of our facilities are fully utilized.

In addition to the above facilities that we use or have used in our operations, we continue to be a named lessee on two leases relating to facilities located in California which were formerly used by Tylan General Corporation prior to its acquisition by Millipore in 1997. These leases expire in 2005 and 2006. These lease obligations were assumed by us pursuant to our separation from Millipore. While both of these facilities have been subleased for the remainder of their terms, under the provisions of the sublease arrangements we were not released from the lease obligations by the landlord.

Item 3.    Legal Proceedings.

On March 3, 2003 we filed a lawsuit against Pall Corporation in the United States District Court for the District of Massachusetts alleging infringement of two of the Company’s U.S. patents by a fluid separation device known as the Pall Photo Kleen EZD-2 filter assembly manufactured and sold by the defendant. Our lawsuit also seeks a preliminary injunction preventing the defendant from the manufacture, use, sale, offer for sale or importation into the U.S. of the infringing product. On March 24, 2003 defendant filed an answer denying that its fluid separation device infringed our patents; defendant also filed a counterclaim seeking a dismissal of the Company’s lawsuit, a decree that our patents are invalid and/or not infringed and costs incurred in conducting the litigation. A five day hearing on our motion for a preliminary injunction and on claim construction of our patents that are the subject of the litigation was held from August 6-12, 2003. As of the date of filing this Annual Report on Form 10-K, the Court has not ruled on our motion for preliminary injunction and upon the construction of the claims of our patents in suit.

We are also party to lawsuits arising in the ordinary course of business. We do not believe that these proceedings individually or in the aggregate will have a material adverse effect on our financial condition, results of operations or cash flows.

Item 4.    Submission of Matters to a Vote of Security Holders.

This item is not applicable.

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PART II

Item 5.    Market for Mykrolis’ Common Stock, and Related Stockholder Matters.

Mykrolis’ Common Stock, $0.01 par value, has traded on the New York Stock Exchange under the symbol “MYK” since August 10, 2001. The following table sets forth, for the indicated fiscal periods, the high and low sales prices of Mykrolis’ Common Stock (as reported on the New York Stock Exchange Composite Tape). As of February 1, 2004 there were approximately 2,313 shareholders of record.

The Company has never declared or paid any cash dividends on its capital stock. The Company currently intends to retain all available earnings for use in its business and does not anticipate paying any cash dividends in the foreseeable future. On November 29, 2001 the Mykrolis Board of Directors declared a dividend of one common stock purchase right for each share of Mykrolis Common Stock outstanding to shareholders of record on December 31, 2001, payable on January 4, 2002. For a description of the Common Stock Rights Plan see “Other Information” in Item 1 above. Each right entitles the holder to purchase one share of Mykrolis Corporation Common Stock at a price of $130.

On October 27, 2003, we acquired the business and certain of the assets and liabilities of Aeronex, Inc. in exchange for cash and 333,333 shares of our common stock. The common stock issued in this transaction was sold in reliance upon the exemption from registration set forth in Section 4(2) of the Securities Act of 1933 relating to sales by an issuer not involving any public offering. Pursuant to the terms of the Aeronex acquisition agreement, the shares issued in this transaction have been deposited in escrow for a period of one year following the closing date to secure certain of the sellers’ obligations thereunder. In addition, we agreed to prepare and file a registration statement on Form S-3 covering those shares for resale on or before the first anniversary of the closing date.

Item 6.    Selected Financial Data.

The following table sets forth selected historical financial information derived from our audited consolidated and combined balance sheets and statements of operations as of and for the years ended December 31, 2003, 2002, 2001, 2000 and 1999 . Our combined financial statements for periods prior to March 31, 2001 include amounts that have been derived from the consolidated financial statements and accounting records of Millipore using the historical results of operations and historical basis of assets and liabilities of our business. The selected historical financial information includes allocations of Millipore corporate expenses related to our business, including centralized research and development, legal, accounting, employee benefits, officers’ salaries, real estate, insurance, information technology services, distribution, treasury and other Millipore corporate and infrastructure costs. These expense allocations were determined on a basis that Millipore and we considered to be a reasonable reflection of the utilization of services provided or the benefit received by us. However, the consolidated and combined financial information included herein may not necessarily reflect our operating results, financial position and cash flows in the future or what they would have been had we been a separate, stand-alone entity during all periods presented.

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You should also read our “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and our consolidated and combined financial statements and related notes included elsewhere in this document for a further explanation of the financial data summarized here